An armoured personnel carrier (APC) is a broad type of armoured, military vehicles designed to transport personnel and equipment in combat zones. They are sometimes referred to colloquially as "battle taxis" or "battle buses". Since World War I, APCs have become a very common piece of military equipment around the world.

According to the definition in the Treaty on Conventional Armed Forces in Europe, an APC is "an armoured combat vehicle which is designed and equipped to transport a combat infantry squad and which, as a rule, is armed with an integral or organic weapon of less than 20 millimetres calibre."[1] Compared to infantry fighting vehicles, which are also used to carry infantry into battle, APCs have less armament and are not designed to provide direct fire support in battle.

The genesis of the armoured personnel carrier was on the Western Front of World War I. In the later stage of the war, Allied tanks could break through enemy lines, but the infantry following—who were needed to consolidate the gains—still faced small arms and artillery fire. Without infantry support, the tanks were isolated and more easily destroyed. In response, the British experimented with carrying machine-gun crews in the Mark V* tank, but it was found that the conditions inside the tanks rendered the men unfit for combat. Britain therefore designed the first purpose-built armoured troop transport, the Mark IX, but the war ended before it could be put to use.

During the Cold War, more specialized APCs were developed. The United States introduced a series of them, including successors to the wartime Landing Vehicle Tracked; but the most prolific was the M113 armored personnel carrier, of which more than 80,000 were produced.[2] Western nations have since retired most M113s, replacing them with newer APCs, many of these wheeled. The Soviet Union produced the BTR-40, BTR-152, BTR-60, BTR-70, BTR-80 in large numbers. Czechoslovakia and Poland together developed the universal amphibious OT-64 SKOT. A cold war example of a "Kangaroo" is the heavily armoured Israeli Achzarit, converted from captured T-55s tanks.

Wheeled vehicles are typically faster on road and less expensive, however have higher ground pressure which decreases mobility offroad and makes them more likely to become stuck in soft terrains such as mud, snow or sand.[3]

Tracked vehicles typically have lower ground pressure and more maneuverability off road. Due to the limited service life of their treads, and the wear they cause on roads, tracked vehicles are typically transported over long distances by rail or trucks.[3]

Many APCs are amphibious, meaning they are able to traverse bodies of water. To move in water they will often have propellers or water jets, or be propelled by their tracks. Preparing the APC to operate amphibiously usually comprises checking the integrity of the hull and folding down a trim vane in front. Water traverse speed varies greatly between vehicles and is much less than ground speed. The maximum swim speed of the M113 is 3.6 mph (5.8 km/h),[4] about 10% its road speed, and the AAVP-7 can swim at 8.2 mph (13.2 km/h).

In "open top" mounts the gunner sticks out of the vehicle and operates a gun on a pintle or ring mount. A ring mount allows the gun to traverse 360 degrees, a pintle mount has a limited field of fire. It can be preferable to an enclosed gunner because it allows a greater field of view and communication using shouts and hand signals. However, the gunner is poorly protected and at risk of injury in the event of vehicle rollover. During the Vietnam War, M113 gunners often suffered heavy casualties.

Enclosed vehicles are equipped with turrets that allow the crew to operate the weapons system while protected by the vehicle's armour. The Soviet BTR-60 has an enclosed turret mounted with a KPV heavy machine gun with a PKT coaxial machine gun. The American AAVP machine gun in a fully enclosed turrets. The AAVP7 mounts an M2 and a Mk 19 grenade launcher in a turret. Turrets typically have optics which make them more accurate.

APCs may be used as armoured ambulances, to conduct evacuations of wounded personnel. These vehicles are equipped with stretchers and medical supplies.

According to article 19 of the Geneva Conventions,[5] "mobile medical units of the Medical Service may in no circumstances be attacked, but at all times be respected and protected by the Parties to the conflict". Although article 22 allows them to carry defensive weaponry, they are typically unarmed. Under Article 39, the emblem of the medical service "shall be displayed ... on all equipment employed in the Medical Service." As such, armoured ambulances will be marked with ICRC recognized symbols.

The infantry fighting vehicle (IFV) is a derivative of the APC. Various classes of infantry fighting vehicles may be deployed alongside tanks and APCs, in armoured and mechanized forces. The fundamental difference between an APC and IFV, is the role they are designed to serve. The CFE treaty stipulates an infantry fighting vehicle is an APC with a cannon in excess of 20 mm, and with this additional firepower the vehicle is more involved in combat, providing fire support to dismounted infantry.

"Infantry mobility vehicle" (IMV) is a new name for the old concept of an armoured car, with an emphasis on mine resistance. They are primarily used to protect passengers in unconventional theatres of war.

The South African Casspir was first built in the late 1970s. In the 21st century, they gained favour in the post-Soviet geopolitical climate. Identical to earlier Humvees in design and function, the uparmoured M1114 is a clear example of this. The addition of armour grants protection to passengers. M1114s have been largely replaced by purpose-built MRAP vehicles.

IMVs generally feature a v-shaped underbelly designed to deflect mine blasts outwards, with additional crew protection features such as four-point seat belts, and seats suspended from the roof or sides of the vehicle. Many feature a remote weapon system. Usually four-wheel drive, these IMVs are distinct from 8-, 6-, and 4-wheeled APCs (such as the VAB), being closer in appearance to civilian armoured money transporters.